This invention relates to a fine particle analyzing device and, more particularly, to a fine particle analyzing device suitable for analyzing a fine particle in a low-pressure sample gas which is, for example, in a process chamber in a semiconductor manufacturing process.
FIG. 5 is a diagram of a known fine particle analyzing device disclosed in Japanese Patent Laid-Open No. 2-190744. In FIG. 5, a introduction tube 2 is inserted at one end of a chamber 1 filled with a sample gas (SG), in which fine particles to be analyzed may be included, for introducing the sample gas from the chamber 1. Also, the tube 2 is connected at the other end to an analyzer tube 5 made of quartz. The analyzer tube 5 extends through a cavity 4 over the entire length of the cavity 4. A microwave source 3 is disposed for emitting a microwaves into the cavity 4. Connected to the other end of the analyzer tube 5 is a spectroscope 7 for analyzing the fine particles in the sample gas qualitatively and quantitatively. The cavity 4 is a thin can-shaped member filled with a cooling medium of a suitable fluid such as dry air. Also, a cooling means 4a such as a pipe for supplying a coolant is disposed along the entire circumference of the cavity 4. A photoelectric transducer 8is electrically connected to the spectroscope 7 in the side opposite to the analyzer tube 5 and a signal processing device 9 is electrically connected to the photoelectric transducer 8. The signal processing device 9 comprises an amplifier 9a, an analog-to-digital (A/D) converter 9b and a central processing unit (CPU) 9c.
Perpendicularly disposed to the side wall of the analyzer tube 5 are a carrier-gas intake pipe 5a connected thereto near the introduction tube 2 for introducing a carrier gas CG such as argon or helium into the analyzer tube 5 and a gas exhaust pipe 5b connected near the other end of analyzer tube 5. An exhaust pump 6 is connected to the end of the gas exhaust pipe 5b. A gas in the analyzer tube 5 is exhausted through the gas exhaust pipe 5b by the exhaust pump 6.
In the known fine particle analyzing device as described above, the sample gas SG is introduced from the chamber 1 to the analyzer tube 5 through the capillary tube 2. In the analyzer tube 5, the sample gas SG is mixed with the carrier gas CG such as argon or helium introduced through the carrier-gas intake pipe 5a. Microwave power is applied through the cavity 4 to the mixed gas in the analyzer tube 5 so that a plasma of the mixed gas is generated in the analyzer tube 5. When the plasma is generated, the fine particles in the sample gas SG are dissociated and ionized by the plasma. The ionized fine particles, the sample gas SG and the carrier gas CG respectively emit light with characteristic spectra. Further, these gases are exhausted from the analyzer tube 5 through the gas exhaust pipe 5b and the exhaust pump 6.
The light generated in the analyzer tube 5 is separated into spectral components by the spectroscope 7. Only the separated spectral components having a wavelength within a wavelength range which may be considered to be generated by the ionized fine particles are selected and converted into electric signals, indicating light intensities, in the photoelectric transducer 8. The electric signals are amplified by the amplifier 9a of the signal processing device 9 and converted into light intensity digital signals by the analog-to-digital (A/D) converter 9b. The light intensity digital signals are determined qualitatively on the basis of the wavelengths of the spectral components by the central processing unit (CPU) 9c. Since the sample gas SG is continuously introduced from the chamber 1 into the analyzer tube 5 and exhausted therefrom, the change of the light intensities of the spectral components generated from the fine particles in the sample gas SG in accordance with the lapse of time becomes pulse signals corresponding to each of the fine particles. Therefore, by counting the number of the peaks of the pulse signals, the number of the fine particles can be determined.
In the known fine particle analyzing device as described above, since energy for dissociating the fine particles to be ionized is generated by collisions between the ions and the electrons which have a high kinetic energy in the plasma, when the kinetic energies of the ions and the electrons are low, the fine particles often cannot be dissociated. Based on our original study, if a plasma is to be generated in a suitable known method such as the ECR method or the multipolar magnetic field method in which a plasma for dissociating the fine particles can be generated by the lowest energy in the current art, the plasma cannot be generated at a pressure below, atmost several Torrs (1 Torr is one-760th of one atmosphere.)
However, in most of the process chambers for use in a semiconductor manufacturing process, since the pressure therein for depositing a film or etching a surface of a semiconductor wafer may be low, such as from several mTorr to several ten mTorr. When a process gas including fine particles which are particularly considered to be a cause of the failure of semiconductor devices in the process chamber is directly introduced as the sample gas SG into the known fine particle analyzing device described above as the sample gas SG, since the pressure in the process chamber is much lower than the pressure necessary for dissociating the fine particles, the fine particles cannot be dissociated at all.
Further, sizes of the fine particles vary for example, there are large particles undesirably attaching to a wafer surface to become a direct cause of a conductor breaking or an electrical short-circuit, medium particles resulting in a poor reliability such as from one-third to one-fifth of a width of the conductor pattern and very small particles as failure nuclei. Therefore, the causes of failure are based on the sizes of the fine particles, and information concerning the sizes of the fine particles is very important. However, since it is difficult to gain the information concerning the sizes in the known fine particle analyzing device as described above, it has been estimated from the qualitative analysis. As the spectral components having a wavelength in a wavelength range which may be considered to be generated from the ionized fine particles only are selected by the photoelectric transducer 8, the estimation becomes ineffectual if a fine particle is almost composed of other components. Then, a dust counter and a wafer surface checking device are necessary to obtain information concerning sizes of the fine particles. Further, the sizes of the fine particles need to be estimated statistically from the qualitative data and size data from the dust counter and the wafer surface checking device.
Also, as the analyzer tube 5 is heated by the plasma to more than 2,000.degree. C. and the quartz composing the analyzer tube 5 may be melted, a cooling means 4a as described above should be provided to the analyzer tube 5 for cooling the analyzer tube 5 and it is not easy to cool the analyzer tube 5.